For civilised men this conception of all existence as being of the same order, an order which we might describe from our own more developed standpoint as at once animated and physical, has become so remote and inadequate, that we find it hard to realise how it can ever have been universally accepted as self-evident truth. Physical science, and under its guidance the current thought of civilised men, has come to draw a marked distinction between the great majority of sensible things, which it regards as purely physical, and a minority which exhibit the presence of “consciousness.” Thus has arisen a theory of the division of existence into two great orders, the physical and the psychical, which so dominates our ordinary thought about the world, that all the efforts of philosophers, both spiritualist and materialist, to reduce the two orders once more to one seem powerless to make any impression on the great majority of minds. When we ask what are the distinguishing marks of the physical order as currently conceived, the precise answer we obtain will depend on the degree of scientific attainments possessed by the person to whom our question is addressed. But in the main both current science and everyday thought, so far as it has reflected on the problem, would probably agree as to the following points. (_a_) Physical existence is purely _material_ or _non-mental_, or again is _unconscious_. The exact significance of these predicates is probably rarely clear even to those who make the freest use of them. On the face of it, such epithets convey only the information that existence of the physical kind differs in some important respect from existence of a mental kind; the nature of the difference they leave obscure. Reflection, however, may throw some light on the matter.